模式介紹

外觀模式的思想是隱藏系統的復雜性。

示例

假設餐館的廚房分為三部分，分別放置冷熱食物和飲料的區域。但是你作為顧客的話，並不關心這些。然而服務員知道這些。

顧客

/// <summary>
/// Patron of the restaurant (duh!)
/// </summary>
class Patron
{
    private string _name;

    public Patron(string name)
    {
        this._name = name;
    }

    public string Name
    {
        get { return _name; }
    }
}
 

聲明廚房區域的接口、訂單類

/// <summary>
/// All items sold in the restaurant must inherit from this.
/// </summary>
class FoodItem { public int DishID; }

/// <summary>
/// Each section of the kitchen must implement this interface.
/// </summary>
interface KitchenSection
{
    FoodItem PrepDish(int DishID);
}

/// <summary>
/// Orders placed by Patrons.
/// </summary>
class Order
{
    public FoodItem Appetizer { get; set; }
    public FoodItem Entree { get; set; }
    public FoodItem Drink { get; set; }
}
 

廚房的三個區域

/// <summary>
/// A division of the kitchen.
/// </summary>
class ColdPrep : KitchenSection
{
    public FoodItem PrepDish(int dishID)
    {
        //Go prep the cold item
        return new FoodItem()
        {
            DishID = dishID
        };
    }
}

/// <summary>
/// A division of the kitchen.
/// </summary>
class HotPrep : KitchenSection
{
    public FoodItem PrepDish(int dishID)
    {
        //Go prep the hot entree
        return new FoodItem()
        {
            DishID = dishID
        };
    }
}

/// <summary>
/// A division of the kitchen.
/// </summary>
class Bar : KitchenSection
{
    public FoodItem PrepDish(int dishID)
    {
        //Go mix the drink
        return new FoodItem()
        {
            DishID = dishID
        };
    }
}
 

服務員

/// <summary>
/// The actual "Facade" class, which hides the complexity of the KitchenSection classes.
/// After all, there‘s no reason a patron should order each part of their meal individually.
/// </summary>
class Server
{
    private ColdPrep _coldPrep = new ColdPrep();
    private Bar _bar = new Bar();
    private HotPrep _hotPrep = new HotPrep();

    public Order PlaceOrder(Patron patron, int coldAppID, int hotEntreeID, int drinkID)
    {
        Console.WriteLine("{0} places order for cold app #" + coldAppID.ToString()
                            + ", hot entree #" + hotEntreeID.ToString()
                            + ", and drink #" + drinkID.ToString() + ".");

        Order order = new Order();

        order.Appetizer = _coldPrep.PrepDish(coldAppID);
        order.Entree = _hotPrep.PrepDish(hotEntreeID);
        order.Drink = _bar.PrepDish(drinkID);

        return order;
    }
}

客戶端調用

static void Main(string[] args)
{
    Server server = new Server();

    Console.WriteLine("Hello!  I‘ll be your server today. What is your name?");
    var name = Console.ReadLine();

    Patron patron = new Patron(name);

    Console.WriteLine("Hello " + patron.Name + ". What appetizer would you like? (1-15):");
    var appID = int.Parse(Console.ReadLine());

    Console.WriteLine("That‘s a good one.  What entree would you like? (1-20):");
    var entreeID = int.Parse(Console.ReadLine());

    Console.WriteLine("A great choice!  Finally, what drink would you like? (1-60):");
    var drinkID = int.Parse(Console.ReadLine());

    Console.WriteLine("I‘ll get that order in right away.");

    server.PlaceOrder(patron, appID, entreeID, drinkID);  //Here‘s what the Facade simplifies

    Console.ReadKey();
}

可以看出，顧客之和服務員進行了交互。

總結

外觀模式是復雜系統上的一層簡單覆蓋，使用較為普遍。

源代碼

https://github.com/exceptionnotfound/DesignPatterns/tree/master/Facade

原文

https://www.exceptionnotfound.net/the-daily-design-pattern-facade/

設計模式（10）外觀模式